The present invention relates to hydrophilic polyolefin materials, in particular fibers and/or filaments, and/or nonwovens, and/or nonwoven products produced from a mixture of at least one polyolefin and at least one melt additive containing a fatty acid ester, with the polyolefin materials including a subsequent activation of the fatty acid ester contained in the melt additive on the surface of the polyolefin materials.
Polyolefins, in particular polyethylene, polypropylene, as well as their copolymers have become established as materials for the production of nonwovens.
Typical applications, in which nonwovens of polyolefins are used, include hygiene products (baby and female hygiene, incontinence products), as well as filter materials. When nonwovens are used, for example as top sheet in baby diapers, they will have to be permeable to body fluids, such as, for example, urine. Then, because of the distinctly hydrophobic character of the polyolefins, a hydrophilic treatment will be needed, which occurs preferably later in the form of a so-called topical treatment. In this process, it is common to use aqueous liquors, which contain amphiphilic surface-active substances, preferably cationic (quaternary ammonium salts), anionic (sulfates, phosphates), or nonionic (ethoxylates, esters, alcohols, silicones) components, or formulations from these substances.
U.S. Pat. No. 6,008,145 discloses a formulation for the permanent hydrophilation of polyolefin fibers, polyolefin filaments, and textiles made therefrom with the use of quaternary ammonium compounds.
According to U.S. Pat. No. 963,929 and DE 196 45 380, nonionic surfactants are used in combination with cationically modified polydimethyl siloxane.
U.S. Pat. No. 6,028,016 discloses a formulation and a method for making nonwovens permanently wettable, with the formulation including a viscosity modifier for a purposeful adjustment of the viscosity of normally unusable, surface-active substances, in that an alkylated polyglycoside is used in combination with surface-active substances, for example, mixtures of modified castor oil and sorbitan monooleate.
A further method of hydrophiling polyolefin fibers or polyester fibers is described in DE 198 51 688, which discloses a mixture of polyolefin or polyester, as well as a compound that includes at least one substance from the class of ethoxylated sugar esters.
U.S. Pat. No. 6,211,101 discloses durable hydrophilic fibers and nonwovens made therefrom, which are intended for use preferably in medical and hygiene applications, and wherein the fiber treating agent contains an ampho-ionic surface-active betain and a dicarboxylic acid ester produced from high-molecular hydroxy-fatty acid esters.
In practice, however, it is found that the topical treatment of nonwovens is connected with the following disadvantages:                1. In use, the surface-active substances are washed out by urine and other body fluids, whereby the hydrophilic properties are successively lost.        2. The washed-out surface-active substances interfere with absorption and fluid distributing processes in hygiene products.        3. The distribution of the surface-active substances on the nonwoven often proceeds only irregularly.        
To improve processability of polyolefins, one often uses so-called process auxiliaries as melt additive. In this connection, one uses as “external lubricants,” for example, fatty-acid derivatives which are provided with polar groups. (Ullannn's Encyclopedia of Industrial Chemistry, VCH Weinheim, 5th Ed., Vol. A20, p. 479.)
However, until now such melt additives have not been widely used for a purposeful hydrophilation of polyolefin nonwovens. Because of phase incompatibility, hydrophilic residues migrate to the fiber surface. The migration in the semicrystalline fiber occurs not only in the course of the spinning process, but also after the spinning process.
For the use of hydrophilic melt additives, U.S. Pat. No. 5,439,734 discloses nonwovens with a durable wettability, consisting of a polyolefin with hydrophilic additives, which comprise fatty acids esterified with dihydroxylated polyethylene glycols.
Furthermore, U.S. Pat. No. 5,969,026 discloses wettable fibers and filaments consisting of polymers and incorporated wetting reagents, wherein the polymers are selected from the class of polyolefins, polyesters, and polyamides, and wherein the active substances essentially consist of a glyceride.
U.S. Pat. No. 5,240,985, U.S. Pat. No. 5,272,196, U.S. Pat. No. 5,281,438, U.S. Pat. No. 5,328,951, and U.S. Pat. No. 5,464,691 disclose amphiphilic additives for modifying polyolefins, with the amphiphilic compounds consisting of an A-B-A combination of a central hydrophilic group, for example, polyethylene glycol, linked to two side groups, which are selected from the class of fatty acids or long-chain alcohols.
Also known are from U.S. Pat. No. 5,696,191 and U.S. Pat. No. 5,641,822 surface-migrating, extrudable thermoplastic mixtures, consisting of at least one polyolefin and an additive, with the additive being a polysiloxane graft copolymer with polyalkene oxide side chains. By extruding the mixture, it is possible to produce wettable nonwovens, which continue to have the corresponding properties even after two years.
Likewise known are from US 2002/0019184 polymers with improved hydrophilicity, which are produced by adding a corresponding quantity of an additive consisting of fatty acids esterified with polyethylene glycols.
US 2001/0008965 discloses multicomponent fibers, wherein a first component consists of a hydrophobic polypropylene, and a second component of a blend of a hydrophobic polyolefin and a hydrophilic melt additive, with the second component being disposed at the surface of the fibers.
WO 98/42767 A1, WO 98/42776 A1, and WO 98/42898 A1 disclose a process of making a polyolefin blend with improved compatibility to adhesives and/or coatings. The blend consists of a polyolefin, a migrating amphiphile and a transition metal.
US 2002/0002242 A1 and WO 01/58987 A2 describe a possibility of increasing the surface energy of polymeric substrates by the use of new amphiphilic block copolymers, in that the block copolymers consisting of linear hydrophobic polymers or oligomers and a statistically hyperbranched polymer or oligomer, are treated in full or in part with lipophilic end groups.
U.S. Pat. No. 5,582,904 describes a method and a resultant end product, wherein hydrophobic polyolefin nonwovens are imparted hydrophilic properties. To this end, one adds to the polymer melt a required content of an alkoxylated fatty acid amine, optionally in combination with as much as 60% by weight of a primary fatty acid amide.
Furthermore, WO 00/71789 discloses polypropylene fibers and structures that can be produced therefrom. In this art, a fatty acid monoglyceride is added as melt additive to the polypropylene, and further additives are used in the form of hydrophilicity improvers and antimicrobial substances.
Last but not least, WO 02/42530 discloses fibers, filaments, and nonwovens, which consist of a melt blend of polyolefin and an additive, with the additive being a chemical substance composed of an alkyl chain and a hydrophilic oligomer. The produced nonwovens exhibit a durable wettability, preferably vis-à-vis body fluids.
The hygiene nonwovens that are hydrophilated with melt additives distinguish themselves in particular by a high permanence of the hydrophilic groups on the fiber surface. However, the hydrophilicity level as is achieved by melt additives, is in many cases too low to meet the requirements of the hygiene industry.